The invention concerns a process for checking air pressure in vehicle wheel tires, as known from EP 0 626 911 B1.
The correct air pressure setting in vehicle wheel tires is of major significance for reasons of economic efficiency and driving safety: an incorrectly set air pressure value--i.e. if the actual air pressure is either too high or too low--will cause increased tire wear on the one hand, necessitating early tire changes, as well as an increase in fuel consumption, and will lead on the other hand to an increase in sidewall flexing as a result of which tire temperatures rise very significantly; this may lead to the destruction of the tire even (in particular when the motor vehicle is traveling at high speeds) which frequently causes extremely serious traffic accidents.
For these reasons, tire pressures should/must be checked at regular intervals; in the case of trucks this check should/must be carried out on a daily basis. However, this check is frequently not carried out as measuring tire air pressure is a relatively timeconsuming and even dirty task which also requires a certain degree of technical skill. Therefore, processes are known already, for example from DE 39 30 489 A1, that are used to measure the air pressure in the tires of motor vehicle wheels by means of a pressure sensor located on the motor vehicle wheel and to indicate to the driver by some suitable means the air pressure signal actually measured.
In the generic type process of EP 626 911 B1, the pressure obtaining in the air chamber of the motor vehicle wheel will be measured by means of a pressure measurement device fitted in or on the tire of each motor vehicle wheel; then, an electric signal representative of the measured air pressure value will be output, and, by means of a transmitter device fitted in or on the tire of each motor vehicle wheel (directly on the valve, for example), a data signal comprising at least the measured air pressure value and an identification value will be generated from the electrical signal, and output; then, the data signals output by the transmitter devices will be detected by means of a stationary reception device, or a reception device fitted in the vehicle, and by means of a control unit these data signals will be evaluated. For reasons of data transmission reliability between the transmitter devices and the reception device (protection against interference signals), the reception unit features identification comparison values that are assigned to the respective identification values of the transmitter devices (thus, the identification value and the assigned identification comparison value are either identical or are found to be in a certain relationship towards each other); fiirther processing of the data signal will take place only if the identification value transmitted by the transmitter device and received by the reception device is identical with the identification comparison value of the reception unit or has been assigned to the same. The identification comparison value can be changed in order to allow a (variable) assignment of the positions of the motor vehicle wheels (for instance when changing a tire, or when changing over from summer tires to winter tires and vice versa); to this end, a control unit enables the reception device to be switched over from its normal operating mode--in which air pressure is checked--into a pairing mode, in which the reception device will receive the identification value output by each transmitter device and store this value as an identification comparison value together with the assignment of the respective wheel position. The disadvantage here is that the assignment or definition of the positions of the motor vehicle wheels is very complex and does not happen automatically.